This invention relates to an arrangement for providing wear, damage and soiling protection of the portion of a recording head which is in intimate operative contact and experiences substantially continuous relative movement with a recording medium. More particularly, the present invention relates to such a protective arrangement in recording systems in which the magnetic latent image created on the recording medium by the recording head is developed with dry magnetic toner. The invention has particular application to magnetographic printing systems.
Recent trends in systems employing a magnetic recording medium, such as a tape, in intimate operative contact with and being imaged by a magnetic recording head, have inter alia called for substantially higher speeds of operation. This in turn has led to increased relative contacting movement between the medium and the recording head. As a result, the incidence of wear has become a point of considerably greater concern in such systems.
This concern potentially is compounded severly in those applications in which the magnetic latent image recording on say the tape medium is developed with dry magnetic toner particles, for subsequent transfer to e.g. paper. Such particles are known to accumulate at the recording zone and thus interfere with the recording process. Moreover the toner particles have a grating effect on the recording head if allowed to come into moving contact therewith, such as would be the case for instance if the steps taken in the recording system for cleaning the residual (post-transfer) toner particles from the tape are not completely successful or fail for whatever reason. Experimentally it has been determined that for the speeds now contemplated for movement of the tape medium passed the recording head, i.e., 35 to 55 inches per second, scoring of the recording head begins in as little time as several seconds and usually within a minute or two. For recording head designs in which the recording zone area of the recording elements is especially delicate (e.g. the thickness of the operative portion of the recording elements at the recording zone being on the order of 1/4 mil thick), such as is the case for example with the recording head design found in U.S. Pat. No. 4,025,927 to Nelson, permanent damage to the recording head is experienced in a few minutes without suitable protection.
Solutions have already been proposed to protect the recording head face with an overlay material. See for example U.S. Pat. No. 3,521,295, Column 3, lines 29 through 33. Generally speaking, these solutions involve permanent or semi-permanent attachments to the recording head face and/or are only replaceable by hand. Permanent attachment of the overlay protector material to the recording head leads to a series of undesirable aspects. First of all, and most importantly, the thicker the overlay material, for purposes of providing its own longevity, the farther away the recording medium must be from the actual recording zones of the recording head. This leads to the necessity of higher recording currents for generating sufficient magnetic field strength to adequately influence the magnetic recording medium across this greater distance. Also, lower magnetic gradients result, with corresponding poorer edge definition with regard to the generated character images. This is especially problematical in those cases where high coercivity magnetic materials are employed. It is to be noted that the use of such magnetic materials is especially preferred in recent developments in magnetography. For higher articulate recording head designs, such as the aforementioned patented Nelson head, which are required for example, in high-quality printing applications, the requirement for substantially increased recording currents necessitated by the use of the permanent overlay material leads to excessive heat generation in a very delicate structure, with the predictable result of substantially reduced lifetime of the recording head structure and non-uniform recording of magnetic dots or pixels (both as to size and magnetic strength).
It will be appreciated, too, that the permanently or semi-permanently attached overlay protective arrangements also succomb to wear. As a result the relatively expensive recording head has to be replaced or at the least the overlay has to be removed and replaced. Either way one is faced with a commercially unattractive and expensive alternative.
With regard to the overlay protective arrangements which require replacement or advancement of the protective material by hand, such approaches require diligent monitoring of the total time of operation of the recording system by the consumer/end user as well as require of the end user an inordinate amount of technical knowledge of the recording system in order to perform such a task. The apparent alternative would be to have such tasks performed during servicing of the apparatus, but this too leads to a commercially unattractive solution.
In Electron Design, May 24, 1980, pages 31 and 32, an arrangement is known where the recording head is placed in operative contact with the back (non-operating) side of a mylar-based recording medium and recording is effected by generating magnetic fields through the Mylar to the magnetizable layer on the opposite side of the recording medium, there to be toned by dry toner on said opposite surface. However, it has been learned that such an arrangement, because of the relatively massive thickness of the recording medium, requires a relatively very expensive and rugged recording head to handle the relatively great recording currents needed to compensate for the separation between the recording elements and the magnetizable layer. Such an arrangement has failed to achieve sharp, articulate imaging and lacks good contrast between imaged and unimaged areas on the recording medium, as well as suffers from weak images that directly translate into relatively poor optical density. Additionally the recording medium will soon enough accumulate dust and toner particles on the back side since it isn't a continuously replenished clean surface that is being provided, but rather is the same surface being provided time and time again. As a result, the problem of soiling the recording head and accumulating damaging and undesirable dust and toner particles at the recording zone area cannot practically be avoided.
What is needed and would be highly useful, therefore, is to provide an arrangement which not only is able to protect the recording head from wear and damage, but is readily and automatically replenishable, is simplictically replaceable apart from the recording head and yet is readily engagable in intimate contact with the recording head, is thin enough so as not to adversely affect the recording current requirements (it is well known, for example, that an overlay material even as thin as 1/2 mil will be more than thick enough to severly disrupt the recording function), and which is automatically and readily moveable relative to the recording head and in intimate contact with the recording zone, and which continuously cleans the recording medium as it approaches the recording head and as such protects the head from soiling effects, and such is the principal object of this invention.